Beams

Abstract

A beam is a structural member subject to bending and is probably the most common structural element that designers have to cope with. Bending occurs in a member when a component of load is applied perpendicular to the member axis, and some distance from a support. Bending causes curvature of a member. Commonly, beams are horizontal, and loads vertically downwards. Most beams span between two or more fixed points as shown in figure 7.1a. The types of support were discussed in section 2.5. As with plane trusses there must be at least three reactive forces to put a beam into equilibrium. In figure 7.1a the supports are one pin and one roller, and this is called simply supported. Another common beam type is the cantilever, as shown in figure 7.1b. Here one end is unsupported but the other must be rigidly built-in to prevent rotation. The third reaction force has now become a moment or couple, but more of that later. A simply supported beam can have a cantilever-end as shown in figure 7.1c.